Optical pickup device

ABSTRACT

A first laser source is arranged on a transmitting side of a polarizing beam splitter, while a second laser source is arranged on a reflecting side of the polarizing beam splitter. The splitting surface of the polarizing beam splitter has a film characteristic of substantially transmitting s-polarization component of the laser light having the first wavelength emitted by the first laser source and substantially reflecting s-polarization component of the laser light having the second wavelength emitted by the second laser source. A plate-like beam splitter serves to introduce laser light reflected off of a signal recording medium into an optical detector by directing the laser light away from the optical path in which the laser sources are located. The plate-like beam splitter includes a splitting surface which has a reflectance that is higher than its transmittance.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2005-156941 filed on May 30, 2005, which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical pickup device including afirst laser source which emits laser light having a first wavelength,and a second laser source which is arranged in an optical path apartfrom that of the first laser source and emits laser light having asecond wavelength which differs from the first wavelength. In thisoptical pickup device, each of the laser light rays emitted from thefirst and the second laser source is introduced into a common opticalpath by means of a polarizing beam splitter. The laser light directedinto the common optical path is reflected by a plate-like beam splitterso as to be directed through an objective lens. The laser light is thenconverged by means of the objective lens and irradiated on a signalrecording medium. Laser light reflected off of the signal recordingmedium is transmitted through the plate-like beam splitter and directedto an optical detector.

2. Description of the Related Art

Optical pickup devices which are compatible for performing recording andreproduction using signal recording mediums having different recordingdensities such as DVDs (digital versatile discs) and CDs (compact discs)have been known. A conventional optical pickup device compatible forperforming recording and reproduction using DVDs and CDs may beconfigured using a beam splitter. In such a device, a laser source forDVD and a laser source for CD may be respectively arranged on thereflecting side and on the transmitting side of the splitting surface.Alternatively, in an opposite approach, the laser source for CD and thelaser source for DVD may be respectively arranged on the reflecting sideand the transmitting side. The optical pickup device is configured suchthat laser light emitted from each of the laser sources is directed intoa common optical path by means of the beam splitter and irradiated intoan objective lens. By selecting either of the laser sources depending onthe type of the disc used, the optical pickup device can executerecording and reproduction using DVDs and CDs.

When employing a beam splitter as described above in order to arrangethe laser source for DVD and the laser source for CD in optical pathsapart from one another, a polarizing beam splitter is used as the beamsplitter. In this case, in accordance with the typical filmcharacteristic of the splitting surface of the polarizing beam splitter,i.e., the characteristic that p-polarization transmittance is higherthan s-polarization transmittance, it is configured such that laserlight incident into the reflecting side of the splitting surface of thepolarizing beam splitter is s-polarized, while laser light incident intothe transmitting side of the splitting surface of the polarizing beamsplitter is p-polarized (refer to Japanese Patent Laid-Open PublicationNo. 2003-141769).

A laser diode used as the laser source for DVD or the laser source forCD emits laser light that is linearly polarized parallel to the p-njunction surface of the laser chip. Accordingly, the polarizationdirection of the laser light with respect to the splitting surface ofthe polarizing beam splitter can be set by selecting the orientation(rotating direction) of the laser source for DVD or the laser source forCD.

Further, in a typical optical pickup device, in addition to arranging alaser diode which emits s-polarized laser light on the reflecting sideof the splitting surface of the polarizing beam splitter and arranging alaser diode which emits p-polarized laser light on the transmitting sideof the splitting surface of the polarizing beam splitter, a quarter-waveplate is provided on the upstream side of the objective lens in theoutgoing optical path by which the laser light advances toward the disc.By causing the linear polarization directions of the incoming andoutgoing laser light beams passing through the quarter-wave plate todiffer by 90°, the film characteristic of the splitting surface of thepolarizing beam splitter can be employed to prevent the returning lightreflected off of the disc from reaching back to the laser diode emittinglaser light.

As described in the above-noted Japanese Patent Laid-Open PublicationNo. 2003-141769, in order to achieve downsizing and efficientarrangement of various optical elements in an optical pickup device, alight-receiving optical system and a light-emitting optical system maybe separately provided by a second beam splitter. The second beamsplitter is provided apart from the polarizing beam splitter which isprovided in the common optical path for DVD and CD. The light-receivingoptical system introduces the returning light reflected off of the discinto the optical detector. The light-emitting optical system for laserlight emission includes the polarizing beam splitter, the laser diodefor DVD, and the laser diode for CD.

In an optical pickup device in which a second beam splitter is providedand laser light reflected by the second beam splitter is directedthrough the objective lens, both laser light beams for DVD and CD arereflected by the second beam splitter. Accordingly Light use efficiencyin connection with the splitting surface (reflecting surface) of thesecond beam splitter is higher for s-polarized laser light than forp-polarized laser light.

As described in the above-noted Japanese Patent Laid-Open PublicationNo. 2003-141769, an optical pickup device compatible for performingrecording and reproduction using DVDs and CDs is often designed whilegiving priority to light use efficiency of the DVD optical system overlight use efficiency of the CD optical system, because the emissionoutput intensity obtained using the laser diode of the laser source forDVD often does not include much margin in view of the output intensitydetermined during the design stage.

In order to prioritize light use efficiency of the laser light for DVD,the laser diode for DVD is arranged on the reflecting side of thepolarizing beam splitter such that laser light emitted from the laserdiode for DVD is subjected to s-polarization reflection at the splittingsurface of the polarizing beam splitter, while the laser diode for CD isarranged on the transmitting side of the polarizing beam splitter suchthat laser light emitted from the laser diode for CD is subjected top-polarization transmission at the splitting surface of the polarizingbeam splitter.

When, apart from the polarizing beam splitter for separately arrangingthe first and the second laser sources, the second beam splitter isprovided in the common optical path in order to separate thelight-receiving optical system for introducing light into the opticaldetector and the light-emitting optical system for emitting laser light,the polarized states of the laser light for DVD and the laser light forCD with respect to the splitting surface of the second beam splitter ares-polarized and p-polarized, respectively, or vice versa. Accordingly,at the second beam splitter, when the device design is determined whilegiving priority to light use efficiency of one of the laser lights(laser light for DVD, for example), light use efficiency of the otherlaser light (laser light for CD, for example) is compromised.

The optical pickup device described in the above-noted Japanese PatentLaid-Open Publication No. 2003-141769 is configured such that both thelaser light for DVD and the laser light for CD are reflected at thesplitting surface of the second beam splitter so as to be directed tothe objective lens. The laser light incident on the splitting surface ofthe second beam splitter in s-polarized state, i.e., the laser light forDVD whose light use efficiency is given priority, is reflectedefficiently, while reflection of the laser light incident on thesplitting surface in p-polarized state, i.e., the laser light for CD, isnot efficiently performed.

In order to improve the reflection efficiency of the laser light for CDwhich is incident on the splitting surface of the second beam splitterin p-polarized state in the above-described optical pickup device, it isnecessary to implement a further feature for the film design of thesplitting surface by, for example, arranging the second beam splitter atan angle such that the angle of the splitting surface with respect tothe optical axis of laser light is 30 degrees, which is smaller than 45degrees. This results in increased limitations to freedom in design, aswell as cost disadvantages.

Further, the optical axis on the reflecting side of the polarizing beamsplitter is more strongly influenced by a tilt of the polarizing beamsplitter as compared to the optical axis on the transmitting side of thepolarizing beam splitter. Accordingly, when high importance is placed onlight use efficiency of the DVD optical system and therefore the laserdiode for DVD is arranged on the reflecting side of the polarizing beamsplitter, an optical axis deviation due to a tilt of the polarizing beamsplitter would cause problems in the DVD optical system which requireshigher accuracy in signal recording density as compared to the CDoptical system.

SUMMARY OF THE INVENTION

An optical pickup device according to an aspect of the present inventionincludes a first laser source which emits laser light having a firstwavelength, and a second laser source which is arranged in an opticalpath apart from that of the first laser source and emits laser lighthaving a second wavelength which differs from the first wavelength. Inthe optical pickup device, Each of the laser light rays emitted from thefirst and the second laser source is directed into a common optical pathby means of a polarizing beam splitter. The laser light introduced intothe common optical path is reflected by a plate-like beam splitter so asto be directed through an objective lens. The laser light is thenconverged by means of the objective lens and irradiated on a signalrecording medium. Laser light reflected off of the signal recordingmedium is transmitted through the plate-like beam splitter and directedinto an optical detector. The first laser source is arranged on atransmitting side of the polarizing beam splitter, while the secondlaser source is arranged on a reflecting side of the polarizing beamsplitter. The polarizing beam splitter includes a splitting surfacewhich substantially transmits s-polarization component of the laserlight having the first wavelength and substantially reflectss-polarization component of the laser light having the secondwavelength. The plate-like beam splitter includes a splitting surfacewhich has a reflectance that is higher than its transmittance.

Accordingly, light use efficiency of the laser light from the firstlaser source arranged on the transmitting side of the polarizing beamsplitter can be enhanced while ensuring light use efficiency of thelaser light emitted from the second laser source arranged on thereflecting side of the polarizing beam splitter. As a result, it ispossible achieve a desirable configuration in which the first lasersource arranged on the transmitting side of the polarizing beamsplitter, which is relatively advantageous in terms of optical axisdeviation, is caused to function in correlation with a signal recordingmedium having higher density.

The first wavelength is preferably shorter than the second wavelength.Further, the splitting surface of the polarizing beam splitterpreferably is provided with a film characteristic of substantiallytransmitting p-polarization component of the laser light having thesecond wavelength while substantially transmitting both p-polarizationand s-polarization components of the laser light having the firstwavelength. Moreover, it is preferable to provide, between the firstlaser source and the polarizing beam splitter, a diffraction filterwhich exhibits a diffraction effect with respect to p-polarized laserlight.

Accordingly, light use efficiency of the laser light from the firstlaser source arranged on the transmitting side of the polarizing beamsplitter can be enhanced while ensuring light use efficiency of thelaser light emitted from the second laser source arranged on thereflecting side of the polarizing beam splitter, such that it ispossible to configure the first laser source arranged on thetransmitting side of the polarizing beam splitter, which is relativelyadvantageous in terms of optical axis deviation, to function incorrelation with a signal recording medium having higher density.Further, by providing the above-noted film characteristic, the splittingsurface of the polarizing beam splitter exhibits substantialtransmission of s-polarization component with respect to the laser lightof the first wavelength emitted from the first laser source whileexhibiting substantial reflection of s-polarization component withrespect to the laser light of the second wavelength emitted from thesecond laser source. According to the above-noted film characteristic,although the splitting surface is limited in connection with the laserlight of the first wavelength in that the splitting surface mustsubstantially transmit the s-polarization component, no designlimitations are created in relation to transmittance of thep-polarization component. Accordingly, it is sufficient to simplyconfigure the splitting surface to substantially transmit bothp-polarization and s-polarization components in connection with thelaser light of the first wavelength, such that impediments to filmformation of the splitting surface are avoided.

Accordingly, both the laser light of the first wavelength and the laserlight of the second wavelength are reflected by the plate-like beamsplitter by virtue of s-polarization. Accordingly, light use efficiencycan be enhanced for both laser light beams. In addition, the splittingsurface of the plate-like beam splitter need simply be characterized tohave a reflectance higher than its transmittance, resulting in minimizeddesign limitations of the splitting surface, high freedom in thearrangement angle of the plate-like beam splitter, and cost advantages.

Accordingly, laser light which has been passed through a quarter-waveplate in both the outgoing and incoming paths is returned to thesplitting surface of the polarizing beam splitter with p-polarizationbeing its main component, such that the returned laser light transmitsthrough the polarizing beam splitter. By providing the diffractionfilter for diffracting p-polarization between the first laser source andthe polarizing beam splitter, it is possible to prevent the returnedlaser light from interfering with the laser light emitted from the firstlaser source.

Moreover, by providing the diffraction filter, the laser light of thesecond wavelength emitted from the second laser source is prevented fromreaching the first laser source. It is therefore possible to prevent thelaser light of the second wavelength from being reflected by an endsurface of the laser chip of the first laser source and subsequentlypenetrating back into the outgoing optical system of the laser light ofthe second wavelength.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an optical arrangement in an examplaryembodiment of an optical pickup device.

FIG. 2 is a side view of the optical arrangement in the optical pickupdevice of FIG. 1.

FIG. 3 is a characteristic diagram showing a film characteristic of asplitting surface of a polarizing beam splitter.

FIG. 4 is a characteristic diagram showing a film characteristic of asplitting surface of a plate-like beam splitter.

FIG. 5 is a diagram explaining a main light-receiving region and two sublight-receiving regions of an optical detector.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIGS. 1 and 2 are plan and side views of an optical arrangement employedin an examplary embodiment of an optical pickup device according to anaspect of the present invention. The optical pickup device shown inFIGS. 1 and 2 is configured to be capable of performing recording andreproduction using CDs as well as DVDs.

A first can-package type laser diode 1 serving as the first laser sourceemits laser light having a first wavelength within the range from650-665 nm (e.g., 660 nm) which is in the red wavelength region andappropriate for performing DVD recording and reproduction. A secondframe-package type laser diode 2 serving as the second laser sourceemits laser light having a second wavelength within the range from775-795 nm (e.g., 785 nm) which is in the infrared wavelength region andappropriate for performing CD recording and reproduction. The first andthe second laser diodes 1, 2 are selectively used in accordance with thedisc type. It should be noted that the package types of the first andthe second laser diodes 1, 2 are not limited to those described above.

The laser light having the first wavelength emitted from the first laserdiode 1 is split into three light beams by a diffraction grating 3 whichexhibits an effective diffraction effect with respect to the firstwavelength of the laser light. The three beams include, in addition to azero diffraction beam, positive and negative first diffraction beamsrequired for tracking control. The diffraction grating 3 is formed bylaminating two cover glass plates. A three-beam splitting grating isprovided on the cover glass plate on the incident side and held betweenthe two cover glass plates, to form a diffraction filter 3 a fordiffracting p-polarization.

The laser light split into three beams by the diffraction grating 3 isdirected to the transmitting side of a polarizing beam splitter 4 havinga prism shape.

The laser light having the second wavelength emitted from the secondlaser diode 2 is split into three beams of zero diffraction beam andpositive and negative first diffraction beams by a diffraction grating 5which exhibits an effective diffraction effect with respect to thesecond wavelength of the laser light. Subsequently, magnification of thesplit laser light is adjusted by a coupling lens 6. This adjusted laserlight is then directed to the reflecting side of the beam splitter 4.

The splitting surface 4a of the polarizing beam splitter 4 ischaracterized as shown in FIG. 3. As shown, the splitting surface 4 ahas a film characteristic of substantially transmitting s-polarizationcomponent of laser light having the first wavelength which is 660 nm,and substantially reflecting s-polarization component of laser lighthaving the second wavelength which is 785 nm. Furthermore, also as shownin FIG. 3, the splitting surface 4 a substantially transmitsp-polarization component of laser light having the first wavelength, andsubstantially transmits p-polarization component of laser light havingthe second wavelength.

In other words, the splitting surface 4 a of the polarizing beamsplitter 4 exhibits substantial transmission with respect to laser lightof the first wavelength without differentiating between p-polarizationand s-polarization, while, with respect to laser light of the secondwavelength, substantially reflecting s-polarization and substantiallytransmitting p-polarization. More specifically, the splitting surface 4a of the polarizing beam splitter 4 exhibits transmittance ofapproximately 96% with respect to laser light of 660 nm for bothp-polarization and s-polarization, while exhibiting, with respect tolaser light of 785 nm, transmittance of approximately 4% (reflectance ofapproximately 96%) for s-polarization component and transmittance ofapproximately 96% for p-polarization component.

As such, the splitting surface 4 a of the polarizing beam splitter 4 hasthe film characteristic of substantially transmitting s-polarizationcomponent of laser light having the first wavelength, and substantiallyreflecting s-polarization component of laser light having the secondwavelength. Accordingly, the first laser diode 1 arranged on thetransmitting side of the polarizing beam splitter 4 is positioned byorienting the p-n junction of the laser chip such that a generated laserlight has the linear polarization direction which is s-polarized withrespect to the splitting surface 4 a. Further, the second laser diode 2arranged on the reflecting side of the polarizing beam splitter 4 isalso positioned by orienting the p-n junction of the laser chip suchthat a generated laser light has the linear polarization direction whichis s-polarized with respect to the splitting surface 4 a.

As a result, the laser light of the first wavelength emitted from thefirst laser diode 1 is substantially transmitted through the splittingsurface 4 a of the polarizing beam splitter 4 after passing through thediffraction filter 3 a provided in the diffraction grating 3. On theother hand, the laser light of the second wavelength emitted from thesecond laser diode 2 is substantially reflected at the splitting surface4 a of the polarizing beam splitter 4.

The laser light of the first wavelength transmitted through thesplitting surface 4 a of the polarizing beam splitter 4 and the laserlight of the second wavelength reflected at the splitting surface 4 a ofthe polarizing beam splitter 4 are directed into a common optical path.The laser light in the common optical path is then reflected by asplitting surface 7 a of a plate-like beam splitter 7 having a parallelflat plate shape, such that the optical axis is bent. Subsequently, thelaser light is reflected by a surface of a bend-up mirror 8, resultingin further bending of the optical axis. The laser light is then formedinto parallel rays by a collimator lens 9, and directed to an objectivelens 11 via a quarter-wave plate 10.

The objective lens 11 is constituted with a bifocal lens compatible withlaser wavelengths for both DVD and CD. The numerical aperture (NA) withrespect to the laser wavelength for DVD is designed to be 0.655, whilethe NA with respect to the laser wavelength for CD is designed to be0.51. When the laser light of the first wavelength emitted from thefirst laser diode 1 corresponding to DVD is directed through theobjective lens 11, this laser light of the first wavelength isirradiated on a signal surface of a DVD by appropriately focusing thelaser light in accordance with the DVD substrate thickness of 0.6 mm. Onthe other hand, when the laser light of the second wavelength emittedfrom the second laser diode 2 corresponding to CD is directed throughthe objective lens 11, this laser light of the second wavelength isirradiated onto a signal surface of a CD by appropriately focusing thelaser light in accordance with the CD substrate thickness of 1.2 mm.

The splitting surface 7 a of the plate-like beam splitter 7 has a filmcharacteristic of substantially reflecting both p-polarization ands-polarization components of laser light regardless of laser lightwavelength, as shown in FIG. 4. More specifically, the splitting surface7 a exhibits transmittance of approximately 8% (i.e., reflectance ofapproximately 92%) with respect to s-polarization, while exhibitingtransmittance of approximately 18% (i.e., reflectance of approximately82%) with respect to p-polarization.

Accordingly, both the laser light of the first wavelength and the laserlight of the second wavelength which are directed onto the splittingsurface 7 a of the plate-like beam splitter 7 in s-polarized state bythe polarizing beam splitter 4 are mostly reflected, at 92% reflectance,so as to be directed to the objective lens 11.

As a result, with respect to the laser light of the first wavelength forDVD, transmittance of 96% at the splitting surface 4 a of the polarizingbeam splitter 4 and reflectance of 92% at the splitting surface 7 a ofthe plate-like beam splitter 7 can be attained, thereby ensuring highlight use efficiency.

Similarly, with respect to the laser light of the second wavelength forCD, reflectance of 96% at the splitting surface 4 a of the polarizingbeam splitter 4 and reflectance of 92% at the splitting surface 7 a ofthe plate-like beam splitter 7 can be attained, thereby ensuring highlight use efficiency.

The laser light converged by the objective lens 11 and irradiated on thesignal surface of the DVD or CD are modulated and reflected by thesignal surface so as to be re-directed through the objective lens 11.This light travels back in the optical path identical to the outgoingpath, that is, the optical path proceeding via the quarter-wave plate10, the collimator lens 9, and the bend-up mirror 8, so as to reach theplate-like beam splitter 7.

The quarter-wave plate 10 is broadband compatible, and serves to apply ashift in the polarization direction (in other words, the phasedifference) by a quarter wavelength with respect to both the laser lighthaving the first wavelength and the laser light having the secondwavelength. Accordingly, both the laser light having the firstwavelength and the laser light having the second wavelength aresubjected to a quarter wavelength shift (in other words, phasedifference of 90°) by the quarter-wave plate 10 in the outgoing path soas to be circularly polarized, and irradiated on a disc in thecircularly polarized state. The laser light reflected off of the disc isfurther subjected to a quarter wavelength shift (in other words, phasedifference of 90°) by the quarter-wave plate 10 in the incoming path, soas to be linearly polarized in a polarization direction which differs by90° from the polarization direction in the outgoing path.

Consequently, in the incoming path, both the laser light having thefirst wavelength and the laser light having the second wavelength becomep-polarized with respect to the splitting surface 7 a of the plate-likebeam splitter 7. By virtue of the p-polarized state, the laser light istransmitted through the plate-like beam splitter 7 at 18% transmittance.The laser light transmitted through the plate-like beam splitter 7 issubsequently imparted with astigmatism for focus control by providing aparallel flat plate 12 arranged at a predetermined angle (in the presentexample, tilted at an angle of 32.5°) with respect to a planeperpendicular to the optical axis of the laser light. The laser lightimparted with astigmatism is directed onto an optical detector 13.

In the optical detector 13, a single light-receiving section is commonlyemployed as a DVD light-receiving section for use in DVD recording andreproduction and as a CD light-receiving section for use in CD recordingand reproduction. As shown in FIG. 5, the optical detector 13 includes amain light-receiving region 13 a and two sub light-receiving regions 13b, 13 c for receiving the three split beams, respectively. Each of themain light-receiving region 13 a and two sub light-receiving regions 13b, 13 c is subdivided into four segments by two dividing lines that areprovided orthogonal to one another. An output from each of the segmentsof the main and two sub light-receiving regions are used to calculatenot only the main signals for performing DVD and CD recording andreproduction, but also tracking error signals and focus error signalscorresponding to tracking control schemes and focus control schemesappropriate for the respective disc types.

Meanwhile, the laser light of the first wavelength and the laser lightof the second wavelength which enter the splitting surface 7 a of theplate-like beam splitter 7 in p-polarized state in the incoming path arereflected off of the splitting surface 7 a at 82% reflectance so as tobe directed back to the polarizing beam splitter 4. The laser light raysof the first and the second wavelength reaching back to the polarizingbeam splitter 4 are also p-polarized with respect to the splittingsurface 4 a of the polarizing beam splitter 4. The film characteristicof the splitting surface 4 a is such that the splitting surface 4 aexhibits high transmittance of 96% with respect to p-polarized laserlight of both the first and the second wavelength. The incoming laserlight is therefore transmitted through the splitting surface 4 a of thepolarizing beam splitter 4 without being sufficiently attenuated.However, because the diffraction filter 3 a for diffractingp-polarization is included in the diffraction grating 3 arranged infront of the first laser diode 1, the diffraction filter 3 a preventsthe incoming light from reaching the first laser diode 1.

On the other hand, the splitting surface 4 a of the polarizing beamsplitter 4 exhibits low reflectance of 4% with respect to p-polarizedlaser light of both the first and the second wavelength. Accordingly,the incoming laser light reflected off of the splitting surface 4 a ofthe polarizing beam splitter 4 is sufficiently attenuated.

As such, in the present embodiment, laser light is prevented fromreaching back to the laser diode originally emitted the laser light tocause interference. At the same time, it is possible to preventoccurrences in which laser light reflected off of a laser chip endsurface of a laser diode (which differs from the one that originallyemitted the laser light) reaches back to the originally-emitting laserdiode to cause interference.

It should be noted that the plate-like beam splitter 7 transmits, at 8%transmittance, the outgoing laser light of both the first and the secondwavelengths which enter the splitting surface 7 a in s-polarized state.In other words, each laser light emitted from the first laser diode 1 orthe second laser diode 2 includes a leak component which is leaked inthe transmitting direction of the plate-like beam splitter 7, apart fromthe main component which advances toward the objective lens 11. Thepresent embodiment is configured such that the leak component of thelaser light is received by a front monitor diode 14. With thisarrangement, the front monitor diode 14 receives the emitted one of thelaser light having the first wavelength or the laser light having thesecond wavelength. Based on an amount of laser light received by thefront monitor diode 14, it is possible to control drive signals fordriving the first and the second laser diode 1, 2. In this manner, theamounts of laser light emitted by the first and the second laser diodes1, 2 can be controlled to prescribed amounts.

It will be obvious to those having skill in the art that many changesmay be made in the above-described details of the examplary embodiments.The scope of the present invention, therefore, should be determined bythe following claims.

1. An optical pickup device, comprising: a first laser source whichemits laser light having a first wavelength; and a second laser sourcewhich is arranged in an optical path apart from that of the first lasersource and emits laser light having a second wavelength which differsfrom the first wavelength; wherein the optical pickup device isconfigured such that each of the laser light rays emitted from the firstand the second laser source is directed into a common optical path bymeans of a polarizing beam splitter, the laser light directed into thecommon optical path is reflected by a plate-like beam splitter so as tobe directed to an objective lens, the laser light is then converged bymeans of the objective lens and irradiated on a signal recording medium,and laser light reflected off of the signal recording medium istransmitted through the plate-like beam splitter and directed to anoptical detector; the first laser source is arranged on a transmittingside of the polarizing beam splitter, while the second laser source isarranged on a reflecting side of the polarizing beam splitter; thepolarizing beam splitter includes a splitting surface whichsubstantially transmits s-polarization component of the laser lighthaving the first wavelength and substantially reflects s-polarizationcomponent of the laser light having the second wavelength; and theplate-like beam splitter includes a splitting surface which has areflectance that is higher than its transmittance.
 2. The optical pickupdevice as defined in claim 1, wherein the first wavelength is shorterthan the second wavelength.
 3. The optical pickup device as defined inclaim 1, wherein the splitting surface of the polarizing beam splitteris provided with a film characteristic of substantially transmittingp-polarization component of the laser light having the second wavelengthwhile substantially transmitting both p-polarization and s-polarizationcomponents of the laser light having the first wavelength.
 4. Theoptical pickup device as defined in claim 1, further comprising: adiffraction filter provided between the first laser source and thepolarizing beam splitter, which exhibits a diffraction effect withrespect to p-polarized laser light.